Magnesium hydroxide has been used in various fields, including applications to an antacid (stomach acid neutralizer), a laxative, a vinyl chloride stabilizer, a ceramic raw material, a heavy oil additive, a flue gas desulfurization agent, a magnesia fertilizer, a food additive (magnesium enhancer), as well as a flame retardant for resins taking advantage of its physical characteristics (utilization of endothermicity at the time of thermal decomposition).
For example, in order to satisfy the flame retardancy requirements for synthetic resins, magnesium hydroxide particles have been attracting attentions. Magnesium hydroxide particles are advantageous in that they have a dehydration onset temperature of about 340° C. and thus are applicable to almost any resin. Further, in PTL 1, a method for synthesizing novel and well crystal-grown magnesium hydroxide particles has been developed. Accordingly, using such a method, it has become possible to obtain an excellent molded article. PTL 1 proposes magnesium hydroxide particles having specific properties such that, as compared with conventional magnesium hydroxide particles, they have less structural distortion, less secondary aggregation of particles, and less residual water molecules and air. It is described that such magnesium hydroxide particles have high affinity with resins such as polyolefins and do not form silver streaks during molding, and thus a molded article with excellent appearance can be obtained, and also that a flame-retardant polypropylene resin molded article that satisfies V-0 of UL94 VE can be obtained.
In addition, PTL 2 proposes a technology in which a flame retardant including magnesium hydroxide particles having an average secondary particle size of 0.4 to 1.0 μm as measured by a laser diffraction scattering method, is used for a polyolefin or a copolymer thereof. PTL 3 proposes a technology in which a certain amount of magnesium hydroxide having an average secondary particle size of 0.01 to 10 μm as measured by a laser diffraction scattering method is blended with hydrotalcite compound particles having specific properties, thereby imparting a suppressing effect on carbon dioxide gas bubbling.